1. Field of the Invention
The present invention relates to a sheet-supply device having a sheet-feed roller for feeding, one at a time, print sheets stacked in a hopper toward a transport roller.
2. Description of the Related Art
There has been known a sheet-feed device including a sheet-feed roller for feeding, toward a transport roller, one sheet at a time from sheets stacked in a hopper. The sheet-feed roller continues rotating until the transport roller picks up the front edge of the fed sheet. Then, the sheet-feed roller stops rotating. Further rotation of the transport roller draws the portion of the sheet remaining in the hopper out of the hopper and transports the sheet toward a print head.
While the transport roller draws the sheet from the hopper, the sheet might fold up or bend and contact the sheet-feed roller. The sheet-feed roller might rotate as a result. When the sheet-feed roller rotates while in its stopped condition in this way, the position of the sheet-feed roller can shift, which makes it difficult to feed subsequent sheets by a predetermined desired amount.
Japanese Laid-Open Patent Publication No. HEI-7-81786 describes an automatic sheet-feed device for ensuring that subsequent sheets can be fed by a desired amount and for preventing two print sheets from being fed at the same time.
Japanese Laid-Open Patent Application No. HEI-7-81786 discloses a sheet-supply device using a sheet-feed roller to feed print sheets one at a time from a hopper containing a plurality of print sheets toward a transport roller, such as a platen roller. The sheet-supply device includes a step motor serving as a rotational drive force source for driving the transport roller; and a drive force transmission mechanism including gears for transmitting rotational drive force from the step motor to the sheet-feed roller. The step motor is capable of selectively driving the transport roller in a forward rotational direction, in which print sheets are transported downstream, or in a reverse rotational direction, in which print sheets are transported upstream. When supplying print sheets using the above-described sheet-feed device, the step motor is first rotated in the reverse rotational direction by a predetermined number of steps to rotate the sheet-feed roller in a sheet-feed direction, whereupon a print sheet is fed to the platen roller. Then, the rotational direction of the step motor is switched to the forward rotational direction. This changes engagement of gears in the drive force transmission mechanism so that the sheet-feed roller and the platen roller are both rotated in the sheet-feed direction.
The device also includes a fixing means for fixing the stopped position of the sheet-feed roller at a predetermined position, with respect to the sheet-feed direction, after the sheet-feed roller is rotated by a predetermined angular amount. The fixing means includes an engagement portion provided to the sheet-feed roller and an arm engageble with the engagement portion. When transmission of drive force to the sheet-feed roller is interrupted, the arm engages in the engagement portion, thereby fixing the sheet-feed roller so it can not be rotated by contact with the sheet. When the sheet-feed roller is rotated in the opposite direction, engagement between the engagement portion and the arm is released.
The sheet-feed roller has one section of its periphery flattened so that it has a substantially half-circle shape in cross section. The curved portion contacts the sheet when the sheet-feed roller feeds a sheet toward the transport roller. The flattened portion confronts but does not contact the sheet when the sheet-feed roller is in its stopped condition.
There has been known a device wherein the sheet supplied by the sheet-feed roller is positioned or aligned by abutting its front edge against the platen roller so that the sheet bends upward.